Head for the linear dimension checking of mechanical pieces

ABSTRACT

A gauging or measuring head for the linear dimension checking of mechanical pieces, including a casing ( 1 ), an arm ( 49 ) carrying a feeler ( 67 ) for contacting a piece to be checked, a fulcrum ( 74 ), coupled to the casing ( 1 ) and the arm ( 49 ), for enabling displacements of the arm ( 49 ) with respect to the casing ( 1 ), a return spring ( 95 ) for keeping the feeler ( 67 ) in contact with the piece during the checking, a device ( 98, 100 ) for retracting the arm ( 49 ) and a position transducer providing signals depending on the position of the arm ( 49 ) with respect to the casing ( 1 ). The fulcrum is made of a deformable element ( 74 ) including two coupling blocks ( 81, 83 ) and three laminae ( 75, 77, 79 ) permanently secured to the blocks ( 81, 83 ), and substantially arranged in two different planes of a sheaf of planes.

TECHNICAL FIELD

The present invention relates to a head for the linear dimensionchecking of mechanical pieces, including a support element that definesa longitudinal geometrical axis, a movable armset with an arm, movablewith respect to the support element, and a feeler coupled to the arm, afulcrum, coupled to the arm and the support element, for defining arotation axis and enabling limited rotational displacements of the armabout the rotation axis with respect to the support element, and atransducer, coupled to the arm and the support element, for providingsignals depending on the position of the arm with respect to the supportelement.

The invention further relates to a head for the linear dimensionchecking of mechanical pieces, including a support element that definesa longitudinal geometrical axis, a movable armset with an arm, movablewith respect to the support element, and a feeler coupled to the arm, afulcrum, coupled to the arm and the support element, for enablinglimited rotational displacements of the arm with respect to the supportelement, a retraction device coupled to the support element and adaptedto cooperate with the movable arm for bringing the arm to a definiteinoperative position, and a transducer, coupled to the arm and thesupport element, for providing signals depending on the position of thearm with respect to the support element. The invention refers also to aprocess for manufacturing a fulcrum to be utilized in a head for thedimension checking.

BACKGROUND ART

There are known many types of gauging or measuring heads for theinspection of mechanical pieces in benches, transfer lines or in theso-called in-process applications in the course of the machining inmachine tools.

In the known heads, the fulcrum, that couples the movable arm to a fixedsupport and must ensure particularly precise displacements of the arm,is achieved by either a material removal, i.e. a manufacturing processthat involves delicate and costly mechanical machinings, or thearrangement, between the arm and the support, generally by removablecouplings, of suitable devices for allowing arm displacements, i.e. anarrangement also requiring the utmost precision and, consequently,considerable time and costs.

In other heads, like the ones shown in U.S. Patent U.S. Pat. No.3,946,492, an unfixed frame member carrying a feeler arm is movablycoupled to a fixed base by means of a pair of spaced apart parallel leafsprings. The leaf springs allow substantially linear and paralleldisplacements of the feeler arm relative to the base, and render theheads unsuitable for checkings where there is shortage of room, such asin many in-process applications. Among other constructional features,the heads shown in the U.S. patent include retraction/release devices,e.g. with a bellows (FIG. 2) and a lever spring, the former beingmechanically secured on one side to the fixed base and on the other sideto such lever spring. The lever spring is, on its turn, pivotablyconnected to a fixed enclosure of the head, and cooperates with both atrasversal leg integral with the movable arm, and a biasing wire springthat also biases against such transversal leg. The dimensions and shapesof the lever and wire springs have to be precisely dimensioned so thatin a non operative condition the unfixed member is retracted, whereasapplying vacuum to the interior of the bellows, the action of thebiasing wire spring prevails, and the unfixed member is released.

DISCLOSURE OF THE INVENTION

Object of the present invention is to provide a gauging or measuringhead for the linear dimension checking of mechanical pieces thatguarantees high standards of repeatability and accuracy, and is morecompact, versatile and less expensive with respect to the known heads.

This and other objects are achieved by a head according to claims 1 and23.

A further object of the invention is to obtain a precise fulcrum forgauging or measuring heads in a particularly economic, rapid andreliable way.

This and other objects are achieved by a manufacturing process accordingto claim 32.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in more detail with reference to theenclosed sheets of drawings, given by way of non limiting example,wherein:

FIG. 1 is an axonometric view of the casing of a head according to theinvention;

FIG. 2 is a longitudinal cross-sectional view of the head shown in FIG.1;

FIG. 3 is a cross-sectional view of the head of FIG. 2, taken along lineIII—III in the direction of the arrows;

FIG. 4 is a plan view of the head of FIG. 2, when viewed in thedirection of arrow IV;

FIG. 5 is a plan view of the head of FIG. 2, when viewed in thedirection of arrow V;

FIG. 6 is a front view of the head of FIG. 2, when viewed in thedirection of arrow VI, wherein the covers 109 and 143, the gaskets 137and 139, the spacer 141 and the feeler 67 with its associated support 66have been removed;

FIG. 7 is a rear view of the head of FIG. 2, when viewed in thedirection of arrow VII;

FIG. 8 is an enlarged scale axonometric view of an element of the headaccording to the invention;and

FIG. 9 is a longitudinal cross-sectional view of a head according to asecond embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The head shown in FIGS. 1-8, more particularly, a gauging head, includesa parallelepipedon shaped, steel casing 1, that forms a support elementand defines a longitudinal geometrical axis. The casing 1 defines sixfaces 3, 5, 7, 9, 11 and 13.

The lateral faces 5 and 9 are reciprocally parallel and substantiallyplane, the rear face 7 is parallel to the front face 3 and the lowerface 13 is parallel to the upper face 11.

The upper face 11 has six threaded holes 23 and an opening 35 for thepassage to a recess 15.

The lower face 13 has three substantially cylindrical holes that definethree seats 17, 19 and 21.

The front face 3 has four threaded holes 46 and a cylindrical-shapedrecess 43 with a central -substantially oval-shaped- hole 45 for thepassage to recess 15.

The rear face 7 has four threaded holes 47.

A movable armset comprises an arm 49 that is partially inserted incasing 1 and arranged in a direction substantially parallel to thelongitudinal geometrical axis of casing 1. The arm 49 includes a firsttapered-shaped, end portion 51, located inside casing 1, a secondportion 53 with a reduced transversal cross-section, a third portion 55with a substantially parallelepipedon shape, a fourth portion 57 with areduced transversal cross-section, a fifth portion 59 with asubstantially cylindrical shape and two grooves 61 and 63, located nextto the front face 3 of casing 1, and a sixth end portion 65, at theexterior of casing 1, carrying a support 66 for a feeler 67.

The first portion 51 of arm 49 has three threaded holes 68, 70 and 71.

The second portion 53 of arm 49 has a threaded hole 72 and a slot 76.

A plate 73 is coupled to casing 1 by means of a screw screwed into hole72.

A fulcrum 74 (also detailedly shown in enlarged scale in FIG. 8) forenabling limited rotational displacements of arm 49, comprises adeformable element consisting of three steel laminae 75, 77, and 79permanently secured to two blocks 81 and 83 made, for example, of a zincalloy. Die-casting is a process adopted for obtaining this permanentcoupling between elements made of different materials, even though therecan be foreseen other types of processes (for example, welding).

The die-casting process for permanently securing the laminae 75, 77 and79 to blocks 81 and 83 consists in the insertion of the laminae 75, 77and 79 in a die in which there is thereafter injected the meltedmaterial required for manufacturing the blocks 81 and 83. Thus, thelaminae 75, 77 and 79 remain secured to this material once it has cooleddown.

When the fulcrum is under rest conditions, the two blocks 81 and 83 aresubstantially parallel with respect to each other and the laminae 75, 77and 79 form, for example, a 45 degree angle with blocks 81 and 83. Thelaminae 75 and 79 are substantially coplanar, whereas lamina 77 forms anangle of approximately 90 degrees with the other two laminae 75 and 79.In substance, the laminae 75, 79, on the one side, and 77, on the other,lie in two planes (e.g. two mutually perpendicular planes) of a sheaf ofplanes defined by a straight line that represents the axis of rotationof arm 49.

Block 81 is coupled to the third portion 55 of arm 49 by means of twoscrews 84 (FIG. 3), while block 83 is coupled to an inner surface ofcasing 1 in correspondence of face 13, by means of two other screws 86(FIG. 5).

Fulcrum 74 enables arm 49 to perform limited but accurate rotationaldisplacements about an axis perpendicular to the longitudinalgeometrical axis of casing 1 and parallel to the upper and lower faces11 and 13, respectively. These displacements are limited by mechanicallimiting devices obtained, for example, in the manner hereinafterdescribed. A screw 85 (FIGS. 2 and 3), passing through a hole —not shownin the figures— of arm 49 is screwed into casing 1 at a reentering partof casing 1. The abutment of the portion 51 of arm 49 against the headof screw 85 limits the upward rotation of arm 49 (in FIG. 2 in acounterclockwise direction). The abutment of a dowel 91 (FIG. 3)—screwed into the threaded hole 70 in arm 49 at the first portion 51—against casing 1, at a surface 87, limits the downward rotation of arm49 (in a clockwise direction in FIG. 2). A biasing device for urgingfeeler 67 against the surface of a mechanical piece to be checkedcomprises a return spring 95, inserted in seat 19 and having an endcoupled to a cover 94 and the other end coupled to an adjustable dowel97 screwed into hole 71. Cover 94 is pulled by return spring 95 againsta recess of seat 19 for sealing seat 19. The coupling between spring 95and dowel 97 includes an idle pin 96, coupled to dowel 97, for settingthe tractive force of the spring 95 (as hereinafter more detailedlydescribed) and preventing it from twisting. This return spring 95applies to arm 49 a moment of rotation in a clockwise direction, inorder to keep the feeler 67 urged against a mechanical piece to bechecked.

A pneumatically-operated retraction device to bring the arm 49 to adefinite inoperative position is made as follows. In seat 17 there islocated a cylinder 98. A piston 100 can slide inside cylinder 98 andcomprises two circular seats 99 for housing gaskets and an end portionfor traversing arm 49 through slot 76 and contacting plate 73. Acompression spring 101 has its ends coupled to piston 100 and casing 1,respectively. A cover 102 is fixed to casing 1 by an elastic ring 103,partially housed in a recess of seat 17, and seals seat 17. Cover 102has an opening for the connection with a tube 93 for the inlet of aircoming from a known pneumatic circuit including a source 92 ofcompressed air.

A similar retraction device may be connected to a known hydrauliccircuit to be hydraulically operated.

A differential transducer of the inductive type comprises windings 105and a core 107 made of ferromagnetic material. The windings 105 arecoupled to casing 1 inside seat 21. A stem 104 is screwed to arm 49 inthreaded hole 68 and inserted in seat 21 of casing 1. Core 107 iscoupled to an end of stem 104 so as to be arranged within windings 105and accomplish (with stem 104) limited displacements, substantiallytranslations, when arm 49 displaces.

A cover 116 is coupled to face 13 of casing 1 by means of screws and hasan opening (not shown in the figures) for the passage of a cable 119(FIG. 5) carrying the electric wires connected to the windings 105 ofthe transducer.

A cover 109 with three holes 111, 113 and 115 is coupled to face 11 ofcasing 1 by means of screws placed in threaded holes 23.

Hole 111 provides access to screw 85 for setting the limit stop of theupper stroke of arm 49. In fact, by screwing or unscrewing screw 85 itis possible to lower or raise the head of screw 85, that, as previouslydescribed, represents the upper limit stop to the rotationaldisplacement of arm 49.

Hole 113 provides access to dowel 91 for setting the limit stop of thelower stroke of arm 49. In fact, by rotating the dowel in one or in theopposite direction, it is possible to make the other end of dowel 91move away from or approach to the surface 87 of casing 1 and, hence,vary the stroke that arm 49 performs before dowel 91 touches the surface87 of casing 1.

Hole 115 provides access to dowel 97 for setting the tractive force ofspring 95. In fact, by operating dowel 97, by virtue of the presence ofthe idle pin 96, that translates without rotating, it is possible tolengthen or shorten spring 95 without twisting it, and thus set thetractive force that spring 95 applies to arm 49.

A toroidal-shaped gasket 117 (or “o-ring”) is placed between cover 109and casing 1 partially housed in a groove of cover 109. A firstflexible, sealing gasket 137 —with a tubular shape— has an end coupledto arm 49, at groove 61, and the other end coupled to casing 1 at agroove 140 defined in the circular opening 43. A second flexible,sealing gasket 139 has an end coupled to arm 49, at groove 63, and theother end coupled to casing 1 at groove 140. A spacer 141 is housed ingroove 140 and separates the ends of the two gaskets 137 and 139. Thefirst gasket 137, made of rubber, has the purpose of protecting theinside of casing 1 from any foreign matter that could affect theperformance of the transducer, while the second gasket 139, made ofrubber calendered into fabric, has the purpose of protecting the firstgasket 137 from possible swarf, that could damage it.

A cover 143 is coupled to face 3 by means of four screws placed in thethreaded holes 46.

The four holes 47 on face —7 are provided for securing the head to asupport (that is not shown in the figures), whereto there can be coupleda second head in the event that, owing to the type of checking operationto be performed, there is the need to utilize two gauging heads. Thegauging head operates in the following way.

Before moving the head and a workpiece to be checked towards each otherin a known way, in order to prevent the feeler 67 from impacting againstthe workpiece or other obstacles during such movement, the arm 49 isbrought to a definite inoperative position in which the feeler 67 is farfrom the checking position. To this end, the retraction device isactivated by making air, coming from source 92, flow inside through tube93. The pressure that the air applies to the piston 100 urges it todisplace upwards, against the bias of spring 101, until it, through slot76, abuts upon plate 73 and thrusts arm 49 to move in counterclockwisedirection (with reference to FIG. 2) until the first portion 51 comes toabutment against the head of screw 85, so defining the inoperativeposition of arm 49.

When a workpiece is placed in the checking position, the retractiondevice is de-energized, by cutting off the air flow and spring 101 drawsthe piston 100 back down. At this moment of time, the tractive force,that spring 95 applies to arm 49, urges the feeler 67 to contact theworkpiece to be checked.

Depending on the position that feeler 67 and consequently arm 49undertake, stem 104 takes a specific corresponding position in seat 21and, therefore, core 107 takes a corresponding specific position withrespect to the windings 105 of the transducer. The electric signalsprovided by the transducer, responsive to the mutual position of core107 and windings 105 and, consequently, to the position taken by feeler67 with respect to a previously set zero position, are sent, throughcable 119, to a storing and processing unit, not shown in the figures,that compares the measurement values with previously memorized nominalvalues. This storing and processing unit can be connected to thenumerical control of the machine tool for the machine feedback.

FIG. 9 shows a head substantially similar to the head of FIGS. 1-7, butincluding a different retraction device comprising a bellows 121,inserted in seat 17. Bellows 121 is made of plastic material, forexample polyurethane, but it may also be made of rubber or of metal.

An end of bellows 121 is clamped in a recess of seat 17 by a flange 125.Flange 125 is fixed, for example screwed, to seat 17, in a known way,not shown in FIG. 9. The clamping of bellows 121 by flange 125 sealsseat 17.

The opposite end of bellows 121 has a closing portion 127 carrying anabutment annular element 129 that is fixed (e. g. glued) at a centralzone of a free surface thereof. Annular element 129 has a cylindricalseat 133 for a corresponding protruding cylindrical element 134 integralwith arm 49.

Flange 125 has a through hole connected to conduits of a known pneumaticcircuit including a source 92 of compressed air.

A return spring 135 is inserted in the folds of the external surface ofthe bellows 121.

The retraction device is activated by making compressed air flow insidebellows 121 through the hole in flange 125. The pressure applied by theair cause the bellows 121 to elongate, in opposition to the tractiveforce of return spring 135, until annular element 129 engagescylindrical element 134 at cylindrical seat 133. The thrust that bellows121 applies to arm 49 urges arm 49 to abut against the head of screw 85.In this way feeler 67 is moved away from the checking position and aninoperative position of arm 49 is defined.

When a workpiece is placed in the checking position, the retractiondevice is de-energized, by cutting off the air flow and the bellows 121is compressed by return spring 135. The air present in bellows 121 flowsback in the pneumatic circuit, through the hole in flange 125.

If bellows 121 is made of metal, it may be fixed, for example glued, toflange 125 and an “o-ring” is used to seal seat 17.

The return spring 135 may have different shape and/or arrangement withrespect to what is shown in FIG. 9, for example it may be arranged inthe folds inside the bellows, or may have coils with smaller diameterand be centrally arranged within the bellows 121, spaced from the insidesurface of the latter. In some cases, depending on the amount of theretraction required and on the material of which the bellows 121 is madeof, the spring 135 may be omitted.

The retraction device shown in FIG. 9 has a particularly simple andeconomic construction, and guarantees substantially friction freeoperations that increase the accuracy and overall realiability of thehead.

The head according to the invention can be utilized for the “in-process”dimension checking of mechanical pieces, in other terms, in the courseof the machining of pieces in a machine tool (for example, a grindingmachine), but also in different applications, for example for“post-process” checkings of pieces, after machining.

The herein provided description and illustrations of a gauging head mayalso apply —substantially without any modifications— to a headperforming absolute measurements. The recess 15 in casing 1 can befilled with oil for ensuring the necessary damping effect on themovements of arm 49 in the event, for example, that it is required toutilize the head for checking grooved pieces. A proper damping effect isin particular obtained by the cooperation of the tapered-shaped endportion 51 of arm 49 with the filling oil.

The fulcrum utilized in the head according to the present invention,that consists of the deformable element 74, has a particularly simple,compact and inexpensive structure. Apart from guaranteeing utmostaccurate displacements of arm 49, fulcrum 74 allows extremely simple andrapid coupling to the reciprocally movable parts (arm 49 and casing 1).

The manufacturing aspects of the deformable element 74 can differ withrespect to what has been herein illustrated and described. For example,the number of laminae can be reduced to two (for example, laminae 75 and77, shown in FIG. 8). Moreover, one of the two laminae can have adifferent shape: more specifically, there can be foreseen an embodimentwherein the two coplanar laminae 75 and 79 are replaced by a singlelamina with a central opening for the passage of lamina 77. Even thearrangement of the laminae can differ, since the reciprocal angularposition and the arrangement with respect to blocks 81 and 83 can vary.In specific applications, there can be foreseen a fulcrum comprising tworeciprocally parallel laminae permanently coupled to blocks 81 and 83.

An advantage offered by the herein illustrated and described head alsoconsists in its specific compactness, by virtue of the absence ofintermediate supports and the coupling of the components (fulcrum,return spring, elements of the transducer and limiting devices) directlyto casing 1. The possibility of reducing to a minimum the layoutdimensions of the head is particularly advantageous in the case of“in-process” applications, where the space available is often limited.

There can be aspects of a (gauging or measuring) head according to theinvention that differ with respect to what has been herein described andillustrated. For example, the retraction can be implemented in adifferent way: by hydraulic or electromagnetic devices or by otherpneumatic devices. There can be utilized even a different type oftransducer with respect to the one herein illustrated and described, andthe biasing and mechanical limit stop devices can be implemented and/orarranged in another way.

What is claimed is:
 1. A head for the linear dimension checking ofmechanical pieces including a support element (1) that defines alongitudinal geometrical axis, a movable armset with an arm (49),movable with respect to said support element (1), and a feeler (67)coupled to said arm (49), a fulcrum (74) coupled to said arm (49) andsaid support element (1), for defining a rotation axis and enablinglimited rotational displacements of said arm (49) about said rotationaxis with respect to said support element (1), and a transducer(105,107), coupled to said arm (49) and said support element (1), forproviding signals depending on the position of said arm (49) withrespect to said support element (1), characterized in that said fulcrum(74) comprises a deformable element with two blocks (81,83) respectivelycoupled to said arm (49) and said support element (1) and arrangedsubstantially parallel with respect to each other, the deformableelement comprising a first lamina (75) and at least a second lamina(77), each of said first (75) and second (77) lamina being permanentlysecured to both blocks (81,83) angularly arranged with respect to bothsaid blocks (81,83) and the other of said first (75) and second (77)lamina.
 2. The head according to claim 1, wherein said first (75) andsecond (77) lamina are made of a material that differs from that of saidblocks (81,83).
 3. The head according to claim 1, including a thirdlamina (79) permanently secured to both said blocks (81,83) andsubstantially coplanar to one of said first (75) and second (77) lamina.4. The head according to claim 3, wherein said first (75), second (77)and third (79) laminae are permanently secured to said blocks (81,83) bydie-casting.
 5. The head according to claim 4, wherein said first (75),second (77) and third (79) laminae are made of steel and said blocks(81,83) are made of zinc alloy.
 6. The head according to claim 1,wherein said support element (1) defines a substantially cylindricalseat (21), and said transducer comprises windings (105) housed in saidseat (21), and a core (107) coupled to and movable with said arm (49).7. The head according to claim 1, including a biasing device locatedbetween said arm (49) and said support element (1) and comprising areturn spring (95) coupled to said arm (49) and said support element(1).
 8. The head according to claim 7, including a device for settingthe biasing force of said return spring (95).
 9. The head according toclaim 1, including two limit stop devices for limiting the displacementsof said movable arm (49) in opposite directions.
 10. The head accordingto claim 9, wherein said limit stop devices comprise a screw (85)screwed to said support element (1) for cooperating with said arm (49),and a dowel (91) coupled to said arm (49) for cooperating with saidsupport element (1).
 11. The head according to claim 10, comprisingdevices for setting said limit stop devices (85,91).
 12. The headaccording to claim 1, including a retraction device (98,100,101) forretracting said movable arm to a definite inoperative position.
 13. Thehead according to claim 12, wherein said retraction device includes apneumatic circuit with a source (92) of compressed air.
 14. The headaccording to claim 13, wherein said retraction device comprises acylinder (98), a piston (100) and a compression spring (101).
 15. Thehead according to claim 13, wherein said retraction device comprises abellows (121) having an end fixed to the support element (1) and anopposite free end adapted to cooperate with the movable arm (49) to urgeit to said definite inoperative position.
 16. The head according toclaim 15, wherein said bellows (121) is connected to said pneumaticcircuit and is adapted to elongate to bring said free end to cooperatewith the movable arm (49).
 17. The head according to claim 16, whereinsaid retraction device further comprises a return spring (135) connectedto said bellows (121) and adapted to apply a compression thrust to it.18. The head according to claim 17, wherein said return spring (135) isinserted in the folds of the external surface of the bellows (121). 19.The head according to claim 15, wherein the bellows (121) is made ofplastic.
 20. The head according to claim 19, wherein the bellows (121)is made of polyurethan.
 21. The head according to claim 15, wherein thebellows (121) is made of metal.
 22. The head according to claim 15,wherein the bellows (121) is made of rubber.
 23. A head for the lineardimension checking of mechanical pieces including a support element (1)that defines a longitudinal geometrical axis, a movable armset with anarm (49), movable with respect to said support element (1), and a feeler(67) coupled to said arm (49), a fulcrum (74) coupled to said arm (49)and said support element (1), for enabling limited rotationaldisplacements of said arm (49) with respect to said support element (1),a retraction device (121) coupled to said support element (1) andadapted to cooperate with the movable arm (49) for bringing the arm (49)to a definite inoperative position, and a transducer (105,107), coupledto said arm (49) and said support element (1), for providing signalsdepending on the position of said arm (49) with respect to said supportelement (1), characterized in that said retraction device comprises abellows (121) having an end fixed to the support element (1) and anopposite free end adapted to cooperate with the movable arm (49) to urgeit to said definite inoperative position.
 24. The head according toclaim 23, wherein said retraction device includes a pneumatic circuitwith a source (93) of compressed air.
 25. The head according to claim24, wherein said bellows (121) is connected to said pneumatic circuitand is adapted to elongate to bring said free end to cooperate with themovable arm (49).
 26. The head according to claim 25, wherein saidretraction device further comprises a return spring (135) connected tosaid bellows (121) and adapted to apply a compression thrust to it. 27.The head according to claim 26, wherein said return spring (135) isinserted in the folds of the external surface of the bellows (121). 28.The head according to claim 23, wherein the bellows (121) is made ofplastic.
 29. The head according to claim 28, wherein the bellows (121)is made of polyurethan.
 30. The head according to claim 23, wherein thebellows (121) is made of metal.
 31. The head according to claim 23,wherein the bellows (121) is made of rubber.
 32. A process formanufacturing a fulcrum (74) to be utilized in a head for the dimensionchecking, comprising the following steps: providing at least two laminae(75,77) made of a first material, obtaining two blocks (81,83) made of asecond material, and permanently securing said laminae (75,77) to saidblocks (81,83) for achieving a single deformable element, wherein thelaminae (75,77) are angularly arranged with respect to each other and tosaid blocks (81,83), and the blocks (81,83) are arranged substantiallyparallel with respect to each other.
 33. The process according to claim32, wherein the step of permanently securing said laminae (75,77) tosaid blocks (81,83) comprises a die-casting process.
 34. The processaccording to claim 33, wherein said at least two laminae (75,77) areinserted in a die, and both the steps of obtaining said two blocks(81,83) and permanently securing the laminae (75,77) to the blocks(81,83) include melting said second material and injecting the meltedsecond material in said die.
 35. The process according to claim 32,wherein said laminae (75, 77) are made of steel and said blocks (81,83)are made of zinc alloy.
 36. The process according to claim 32, whereinthe step of permanently securing said laminae (77,78) to said blocks(81,83) comprises a welding process.